1. Field of the Invention
This invention relates to a digital signal transmitting method, a digital signal receiving apparatus, and a recording medium, and is applicable, for example, to a digital signal transmitting system which provides fee-charged software information to contract users.
2. Description of the Related Art
In a conventional digital signal transmitting system using satellites or cables, as shown in FIG. 1, a program source PS, input to a digital signal transmitting apparatus, i.e., a broadcasting station 1, is band-compression coded with a moving picture image coding experts group (MPEG) method by means of an MPEG encoder 2 and is converted to packet transmission data by means of a packet generation section 3.
The packetized transmission data is multiplexed by a multiplexer 4, then the transmission data is scrambled for security by an encryption processing section 5, and finally keys (ciphers) are put over the scrambled data many times so that the scrambling cannot be descrambled easily. The encrypted transmission data is error corrected by a forward error correction (FEC) section 6 and modulated by a modulator 7. The modulated data is then sent through a digital satellite 8 directly to a digital signal receiving apparatus installed in a contract user""s household, i.e., a terminal 10 (FIG. 2), or sent through the digital satellite 8 to a signal distributing station 9 (FIG. 2) which is called a head end. The data, transmitted to the signal distributing station 9, is sent to the terminal 10 via cable.
Now, as shown in FIG. 2, in the terminal 10, when the transmission data is directly sent via the satellite 8, the data is received by an antenna 11 and sent to a front end section 12. When the transmission data is sent from the signal distributing station 9 via the cable, it is inputted directly to the front end section 12. A user contracting with the broadcasting station 1 accesses a key authorized to each user to the terminal 10, with respect to the transmission data sent directly from the satellite 8 or from the satellite 8 via the signal distributing station 9, so that the user is authorized as a contract user and bill processing is performed, and at the same time, the user can appreciate desired software information.
That is, in the terminal 10, the transmission data is processed by the front end section 12 comprising a tuner, a demodulator, and an error corrector, and the processed data is input to a data fetch section 13. In the data fetch section 13, the multiplexed data is demultiplexed by the demultiplexer 14 so that the data is separated into a video signal, an audio signal, and data other than these signals. In a decryption section 15, ciphers are decrypted while performing bill processing. In a packet separation section 16, the decrypted data is packet separated. Finally, the compression of the data is expanded by an MPEG decoder 17, and the video and audio signals, which are digital-to-analog converted to analog signals, are output to television.
Incidentally, in the digital signal transmission system, when fee-charged software information such as video on demand or near video on demand is transmitted, a digital storage 18 such as tape media or disk media is incorporated into or connected to the terminal 10 to meet the convenience of users and to effectively utilize a digital transmission path. In such a case, large amounts of software data have been downloaded to the storage 18 by making use of an unoccupied time band and an unoccupied transmission path, and when the user looks at the software information at hand, the user accesses it with an ID card (for example, smart card) 19 to perform bill processing, and reproduction limitation is lifted.
More specifically, if the user accesses a central processing unit (CPU) 20 by means of the smart card 19, the CPU 20 performs an inquiry of registration to an authorization center 22 (FIG. 1) through a modem 21. The authorization center 22 confirms registration by means of a conditional access 23. If registration is confirmed, the authorization center 22 performs bill processing and also performs notification of confirmation to the CPU 20 through the modem 21.
The CPU 20 instructs decryption of key to a local conditional access 24 by this notification, and the local conditional access 24 decrypts a cipher which has been put over the data recorded on the storage 18. Hence, the reproduction limitation is lifted, and the packet of the data recorded on the storage 18 is separated by the packet separation section 16. The compression of the packet-separated data is decompressed (expanded) by the MPEG decoder 17 and then the expanded data is digital-to-analog converted to be output to television as the analog signal and audio signal A/V.
However, if, in the security system in a current broadcasting form, software information has been downloaded to the storage 18, as described above, to try to realize a system where this software can be appreciated when user wants to see it, then the following problems will arise.
More specifically, in the current digital signal transmitting system, when a cipher is decrypted by the decrypting section 15 and then software information is downloaded to the storage 18, as shown by point A in FIG. 3, fee-charged software cannot be downloaded to the storage 18 by decrypting the cipher without billing, because decrypting a cipher is, vis-a-vis, billing. Now, if only billing information is made free, all ciphers of data are decrypted, and downloaded to the storage 18, then a piece of software information is passed as it is and output from the terminal 10.
Also, in a case where the storage 18 is not incorporated into the terminal 10 but is connected to the terminal 10 and switching means is not provided between the decryption section 15 and the packet separation section 16, if ciphers are all decrypted and downloaded to the storage 18, then the decrypted data are all sent and there is the possibility that they can been seen for free at point C of FIG. 3 by persons other than contract users.
To solve these problems, data can be downloaded to the storage 18 before ciphers are decrypted, i.e., after multiplex is demultiplexed by the demultiplexer 14 (point B of FIG. 3). If, however, data are downloaded to the storage 18 after multiplex is demultiplexed by the demultiplexer 14, there is the problem that intra-coded (I) pictures can not be pulled out and can not be reproduced at variable speed, because data remain encrypted. Also, in broadcasting systems where data are encrypted, keys are changed annually or biennially to ensure security. Therefore, when a key is changed after software information is downloaded to the storage 18, there is the problem that ciphers cannot be decrypted and therefore the downloaded software information cannot be seen.
In view of the foregoing, an object of this invention is to provide a digital signal transmitting method, a digital signal receiving apparatus, and a recording medium which are capable of ensuring security when fee-charged software information is transmitted.
The foregoing object and other objects of the invention have been achieved by the provision of a digital signal transmitting method where at least a band-compression coded digital video signal is given encryption processing and transmitted, in which when an image providing predetermined services is transmitted, the band-compression coded digital signal is given first-encryption processing and then the first-encryption processed digital signal is further given the encryption processing and transmitted.
Also, according to the present invention, in the digital signal transmitting method where at least a band-compression coded digital video signal is given encryption processing and transmitted, the band-compression coded and encryption processed digital signal is mixed with the digital signal where the band-compression encoding has been completed within a predetermined image unit, and the mixed signal is transmitted.
In addition, according to the present invention, in a digital signal receiving apparatus 40 for receiving at least a band-compression coded digital video signal over which a first cipher is put and then a second cipher is put and which is transmitted by a broadcasting station, the digital signal receiving apparatus comprises second decrypting means 15, 19 for decrypting the second cipher put over the digital signal; recording/reproducing means 73, 74, 75, 76, 77 for recording the digital signal, where the second cipher was decrypted, on a recording medium, and also for reproducing the digital signal recorded on the recording medium; and first decrypting means 46, 91 for decrypting the first cipher of a reproduction signal that is reproduced from the recording medium.
Furthermore, in the present invention, there is provided a recording medium 101 wherein at least a band-compression coded digital video signal has been encrypted and recorded.
When an image providing predetermined services is transmitted, a band-compression coded digital video signal is given first-encryption processing and then the digital signal is further given encryption processing and transmitted. Therefore, double security can be added to the video signal so that a digital signal transmitting method where its security is more firmly ensured can be realized.
Further, at least a band-compression coded and first-encryption processed digital video signal are mixed with the digital signal where the band-compression encoding has been completed within a predetermined image unit in a broadcasting station 30. Therefore, variable-speed reproduction image can be viewed without performing variable-speed reproduction processing at a terminal 40.
When a first cipher and a second cipher are put over a digital signal where at least a video signal was the band-compression coded, and the digital signal which is transmitted by the broadcasting station 30 is received, the second cipher of the received digital signal is decrypted by the second decrypting means 15, 19 and the second decrypted digital signal is recorded on a recording medium by means of recording/reproducing means 73, 74, 75, 77. At the time of reproduction, the first cipher of the reproduction signal which is reproduced from the recording medium is decrypted by the first decrypting means 46, 91. Hence, a digital signal receiving apparatus 40 where its security is more firmly ensured can be realized.
Furthermore, there is provided a recording medium 101 wherein at least a band-compression coded digital video signal has been encrypted and recorded. With this, contract users are able to cheaply obtain the recording medium 101 where a plurality of pieces of encrypted software information are recorded, and are able to construct a new software information supply system where only information that users desire to see is billed and enjoyed.
The nature, principle and utility of the invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings in which like parts are designated by like reference numerals or characters.